Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for communication links to be arranged between mobile end devices. The end devices may be able to communicate through different types of communications, depending on the standard(s) supported by the end devices and network. For example, push-to-talk (PTT) end devices support communication types that include indirect communication, in which a system infrastructure having fixed installations including base transceiver stations (base stations, or as referred to herein, RF sites) and a call control computer/server (also known as a communication or network switch or a mobile switching center) are employed or direct communication between the end devices, in which the system infrastructure is not used.
A variety of modes may be available in each of these communications types. These modes include conventional over-the-air (OTA) device-to-device communication or trunked communication. In trunked communication, a (talk) group call is initially established using a group address to which members of the talkgroup subscribe and then audio is transmitted from the transmitting end device to all receiving end devices that are members of the talkgroup by use of transmitting to the group address.
In a digital trunked radio system, there are a number of scenarios which result in service outages. In non-redundant configurations, if one of the base stations or the call control computer fails or if a communication link between one of the base stations and the switch fails, the resulting catastrophic breakdown terminates communications between the transmitter and one or more of the receivers until either the base station or switch is repaired or the link problems clear up. If a redundant configuration is used in which a second switch is used as a standby switch, communication is stopped for the period it takes to re-route the communication (losing any audio data, which is generally not retransmitted if not received) or re-establish the control communication (as control data is generally retransmitted if not received).
Outages can range from several seconds to hours or more. While such problems may be somewhat inconvenient for most users and applications, there exist situations in which even a relatively short loss of data or delay is unacceptable. One such situation is Mission Critical applications, such as public safety operations at incidents, in which consistent reliability in communications is imperative through severe environmental and operations stresses. It is thus desirable to provide a communication system in which loss of control and other data due to infrastructure device or link failure is eliminated.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.